1. Field of the Invention
This invention relates to tin oxide coated articles, and, more particularly, to transparent, haze-free tin oxide coatings on glass made by chemical vapor deposition.
2. Description of Prior Art
Tin oxide is widely used as a coating material in optical instruments. For example, U.S. Pat. No. 4,497,700 describes the use of tin oxide as an anti-reflective coating in a multi-layer optical filter. This tin oxide coating is required to be transparent and haze-free in order to avoid interference with the optical performance of the device. Similarly, Gordon, in U.S. Pat. Nos. 4,187,336; 4,206,452; 4,308,316; and 4,377,613, uses a tin oxide coating to reduce or cancel iridescence in glass window structures. While such tin oxide coatings function effectively for the purposes intended, they introduce haze into the system unless formed under very restrictive and disadvantageous deposition conditions.
A number of patents are directed to reducing haze in tin oxide coatings, e.g. U.S. Pat. Nos. 2,567,331; 2,614,944; 2,617,741; 3,107,177; 3,677,814; 3,759,743; 4,187,336; 4,329,379; 4,547,400; and 4,548,836. These patents teach the avoidance of tin tetrachloride, or any other similar organotin compound containing a halide, e.g. chlorine, which can produce halogen acid vapors at the hot glass surface. In the event a halide-containing organotin compound is used, it is suggested that hydrazine be included in the coating composition, or that an undercoat layer of a metal oxide, for example, silicon dioxide, precede the tin oxide coating.
Accordingly, it is an object herein to provide an improved tin oxide coated article made by a chemical deposition method, which article is characterized by comprising a transparent, haze-free tin oxide coating on a substrate.
Another object of this invention is to provide haze-free tin oxide coatings on a substrate, such as glass, in which the oxide coating is produced rapidly at an elevated substrate temperature using a liquid coating composition comprising a liquid organotin compound and a haze-reducing additive.
Still another object of the invention is to provide such tin oxide coated articles characterized by including a transparent, haze-free tin oxide coating on a substrate, without requiring an undercoat layer.
A specific object of the invention is to provide a tin oxide coated article which includes a transparent, haze-free tin oxide coating on a glass substrate, which may be formed by chemical vapor deposition from a liquid coating composition.